From: "David F. Ogren" <ogren@cris.com>
Date: Fri, 31 May 1996 20:12:29 +0800
To: cypherpunks@toad.com
Subject: (Fwd) Re: [crypto] crypto-protocols for trading card games
Message-ID: <199605310701.DAA16729@darius.cris.com>
MIME-Version: 1.0
Content-Type: text/plain


-----BEGIN PGP SIGNED MESSAGE-----

Gary Howland asked me to forward his response to the mailing-list:

- ------- Forwarded Message Follows -------
Date:          Thu, 30 May 1996 12:12:48 +0200
From:          Gary Howland <gary@systemics.com>
Organization:  Systemics Ltd.
To:            ogren@cris.com
Subject:       Re: [crypto] crypto-protocols for trading card games

David F. Ogren wrote:

> Cards are not transferrable.  In order to make cards transferrable
> the game company must be able to invalidate cards which have been
> traded to others.  In other words if Alice wants to give a cards to
> Bob she must:
> 
> 1. Contact the game company and tell them she wants to give the card
> to Bob. 2. The game company must issue a new card to Bob with a new
> serial number and with Bob's public key rather than Alice's. 3. The
> game company must invalidate Alice's old card.  Since there is no
> way that the game company can make sure all copies of the card have
> been destroyed it must create a "invalid serial number list" and
> have the players dial into that list everytime the game is played.

This is the double spending problem.

> Since step 3 is so costly to implement, I think it is unlikely that
> a cryptography-based trading card game will have tradable cards.

Given that untraceability of cards is less of an issue than with
e-cash, why not have a central registry of the owners of the cards
(which would consist of the card hashes paired with the public key
fingerprint)?  Admittedly this means the players must be on line, but
then we all know how difficult off line detection of double spenders
is.

For anyone who is _serious_ about starting work on such a game
system, I have a few pieces of Perl and Java code that would really
get you on your way - let me know if you are interested.


Gary
- --
pub  1024/C001D00D 1996/01/22  Gary Howland <gary@systemics.com>
Key fingerprint =  0C FB 60 61 4D 3B 24 7D  1C 89 1D BE 1F EE 09 06



-----BEGIN PGP SIGNATURE-----
Version: 2.6.2

iQCVAwUBMa6YXPBB6nnGJuMRAQG0tgP8DSnhI+SgoaR63AuOpOi7qPgC6Ei3bFJV
TdZUB6lfYg3FnE4AaBkxdYkGPfzoyJx1u3Nu/s2BJs5i3Zd2eOfYohj3CJoXJVo1
04zXamo9cCvgemNTplT331sFc+nX/iOIRUvAWbJdfhaOapnm6KVSrNkFqhiRhQ5S
0SYvgcISnZA=
=VdtP
-----END PGP SIGNATURE-----
--
David F. Ogren
ogren@concentric.net (alternate address: dfogren@msn.com)
PGP Key ID: 0xC626E311
PGP Key Fingerprint: 24 23 CD 15 BF 8D D1 DE  81 71 84 C8 2C E0 4B 01
(public key available via server or by sending a message to
ogren@concentric.net with a subject of GETPGPKEY)